The present invention concerns a sterilizable disposable liner for a pressure, level or temperature measurement instrument for use in industrial applications requiring high standards of hygiene.
There is a wide range of measurement instruments on the market suitable for industrial applications. Measurement instruments comprise a sensing element for sensing a physical quantity of a product in a container and a process connector for mounting the sensing element on a counter connector on a container. In various branches of industry, the measurement data obtained by these devices is used to control complex industrial processes.
At present, pressure measurement instruments are on the market for measuring a pressure of a product in a container. They comprise a sensing element having a diaphragm, which during measurement operation is exposed to the pressure to be measured. A pressure dependent deflection of the diaphragm is either measured directly or is hydraulically transported to a pressure sensor via a pressure fluid.
Also various types of level measurement instruments are on the market. Level measurement instruments can be used for continuous level measurement as well as for determining whether a level of the product is above or below a predetermined level.
One group of level measurement instruments are capacitance level measurement instruments. In capacitance level measurement an electromagnetic signal, for example a radio frequency, is applied to a conductive probe extending into the container and a capacitance between a conductive probe and the container wall is determined. The capacity is a measure for the level of the product inside the container.
Other groups of level measurement instruments apply time of flight measurement techniques. Here a level of the product is determined based on the time of flight needed, for an electromagnetic signal to travel to the surface of the product and for its reflection to return. The electromagnetic signals are for example free radar waves or microwaves, which are send and received via a rod antenna extending into the container, or guided waves traveling along a probe, that extends into the container.
Temperature measurement instruments are available on the market. They usually comprise a probe comprising a temperature sensor, which is exposed to the temperature of the product in the container by insertion of the probe into the container.
Such level, pressure or temperature measurement instruments are for example sold by the applicant. They are on the market for example for measuring a pressure of a product in a pipe, tube or vessel, or a level in a vessel.
In some industries, for example in the Pharmaceutical Industry or in Biotechnology, very high standards of hygiene are required. These standards may vary slightly from country to country, but in general they address or validate, that any surfaces of the instruments, which may come in contact with the process can be effectively cleaned and/or sterilized. In the USA such standards are for example 3-A, ASME/BPE or EHEDG.
In addition, according to the FDA Current Good Manufacturing Practice (CGMP), materials that contact components, in-process materials or drug products shall not be reactive, additive, or absorbtive so as to alter the safety, identity, strength, quality or purity of a drug product beyond the official or other established requirements.
As a consequence all measurement instruments used in these industries must be designed in such a way that any parts in contact with the process can be cleaned and/or sterilized. Widely used methods are Cleaning in Place (CIP) or Sterilization in Place (SIP). Cleaning and/or sterilization can be carried out with automated or manual systems via various procedures on the site in a reliable and repeatable process that meets the stringent hygiene regulations demanded by biotechnology and pharmaceutical industries. Some systems include spray balls which can be permanently installed inside containers to apply liquid cleaners, water, detergents, steam or other cleaning or sterilization agents into closed containers.
The measurement instruments are mounted on process equipment, for example on a process connector on the container. In practice, the complete system, including the measurement instrument, is cleaned in place (CIP'd) and/or sterilized in place (SIP'd). The processing system is run for a period of time. Afterwards it is flushed, cleaned in place and/or sterilized in place before the next batch of product is run through the process. CIP and SIP assures, that there is no adulteration or contamination of the current product due to residual product left in the processing system during the previous product run.
CIP of a processing system can take hours to complete and sterilization can require another hour or even more time. During this time, the equipment and piping system can not be used otherwise. This time is lost for production every time cleaning or sterilization is required, for example due to a change of product or batch. This is very costly, especially when batch times or product cycles are short compared to the time required for cleaning and/or sterilization.
In addition, the chemicals used for CIP are expensive and often dangerous to handle and/or dispose of. Energy is required to heat the cleaning agents to the proper cleaning temperature, typically 120° F. to 160° F. Energy is required to heat the sterilization liquids or steam to a sterilization temperature, typically of 300° F. After the processing system has been cleaned and/or sterilized, additional energy may be required to cool the processing system down to an operating temperature.
There is a need in Industry, to reduce the time needed for cleaning and/or sterilizing dramatically.
At present disposable liners for industrial containers used in production processes are on the market, which can be sterilized prior to insertion in the container. The company HyClone, Logan, Utah, USA for example sells disposable sterilizable containers liner having a capacity ranging from 50 mL up to 1000 L or larger together with customized or standard tubing sets and fittings, for example quick connect, Luer Lock or Tri-Clamp. At the end of a production process, these container liners are removed from the container and are then disposed. A new container liner is inserted prior to the next production process. Since a new container liner can be inserted for every new production process, it is no longer necessary to clean and sterilize the container. The use of a new clean and sterile container liner ensures that the product in the container is exposed to the clean and sterile interior surface of the liner only.
In medical applications the need for cleaning and/or sterilization is overcome to a large extent by disposable parts. U.S. Pat. No. 6,725,726 for example, describes a disposable pressure dome for a reusable pressure transmitter. The pressure dome comprises an inlet channel, an outlet channel and a measurement channel and is removably coupled to the transducer. The inlet and the outlet channel are process connections. The entire dome including these process connections is disposed of after use.
In industrial application containers and measurement instruments are usually expensive parts, which cannot be replaced after every measurement cycle. Process connections of measurement instruments are quite often integral parts of the measurement instrument, which cannot be easily separated from the remaining parts of the instrument. They are standardized massive metal or stainless steel parts. In addition, a replacement of the process connections after every single use would increase the costs of production.
It is an object of the invention to provide means for allowing a time and cost effective use of measurement instruments in industrial applications where high standards of hygiene need to be fulfilled.
To this end the invention comprises a disposable sterilizable liner for a level, pressure or temperature measurement instrument for measuring level, pressure or temperature of a product in a container, for use in combination with a disposable container liner covering an interior of the container,                wherein the measurement instrument comprises:                    a sensing element for sensing a physical quantity, and            a process connector for mounting the sensing element on a counter connector on the container, and                        wherein the liner for the measurement instrument                    is one integral element made out of an elastic material,            has a shape that exactly follows outer contours of the sensing element and the process connector, such that it forms a removable single use hygienic liner for closely covering all surfaces of the measurement instrument exposed to the product during measurement operation, and            comprises a mounting section, which in operation is clamped between the process connector and the counter connector                        
According to a preferred embodiment the sterilizable disposable liner has a thickness of less than one millimeter.
According to a preferred embodiment the disposable sterilizable liner is a foil out of a plastic or elastomeric material, in particular out of polypropylene, polyethylene, polytetrafluoroethylen (PTFE), latex or rubber.
According to another preferred embodiment, a seal for sealing a connection between the process connector and the counter connector is an integral part of the liner.
According to one embodiment, the sensing element comprises a measurement probe and the liner comprises a section for closely covering the probe.
According to another embodiment, the sensing element comprises a rod antenna and the liner comprises a section for closely covering the rod antenna.
According to another embodiment, the sensing element comprises a convoluted diaphragm, and the liner comprises a convoluted section for closely covering the convoluted diaphragm.
The invention further concerns a method of running consecutive production processes using the same level, pressure or temperature measurement instrument and sterilizable, disposable liners according to the invention, comprising the steps of                mounting a previously sterilized disposable liner on the measurement instrument,        mounting the instrument on the container,        running a production process,        disposing of the used liner at the end of the production process, and        repeating these steps for every new production process.        
The invention and further advantages are explained in more detail using the figures of the drawing, in which four exemplary embodiments are shown.